Nitration of para cresol



Patented Nov. 8, 1938 UNITED STATES PATENT OFFICE NITRATION OF PARAC'RESOL No Drawing. Application April 5, 1937, Serial No. 135,107

11 Claims.

Our present invention relates to the nitration of para cresol to formmeta nitro para cresol, expressed as 4-methyl-2-nitro-l-hydroxy-benzene.

Some compounds are readily nitrated by well known procedures, whileothers are not subject to such procedures owing to numerous undesiredresults, such as isomeric nitration, di-nitration, oxidation,resinification, or owing to the effect of the procedure upon impuritiesor isomers accompanying the desired raw material.

Para cresol as such is a fairly expensive raw material, but when mixedwith its meta isomer roughly in the proportion of parts meta to 40 partspara, it is a much less expensive material. At considerable cost fortreatment, the content of the meta isomer may be reduced. Consideringcosts, yields, purities, kinds of nitration processes, and commercialsupplies, specifications, and demands, there is still a place for alow-cost nitrating process operable upon either a pure para cresol orupon an impure para cresol, such as one containing its isomeric forms,particularly the meta cresol, to yield an acceptable grade of meta nitropara cresol.

Para cresol has heretofore offered practical and economic difiicultiesfor low-cost nitration processes. So far as we have been able toascertain, a complicated procedure has been employed heretofore,involving use of solvents, such as ether, and a necessary cooling. Thenitration of cresol offers difliculties not encountered in nitratingphenol. While there is but one form of phenol, there are three isomericforms of cresol. These may or may not react differently to some selectednitration procedure. A procedure which nitrates one isomer may notnitrate another; and where mixed isomers are present, one isomer mayinterfere with nitration of another isomer.

The present invention aims to provide a simple practical and economicprocess for the nitration of para cresol, which may be practiced upon apure para cresol, and also upon mixed cresol isomers to nitrate the paracresol content, and to give in both cases a useful grade of meta nitropara cresol.

A particular object of the invention is the aqueous nitration of cresolcontaining para cresol by the action of an aqueous solution of nitricacid to secure the desired nitration of the para cresol content.

A further object of the invention is the aqueous nitration of cresolcontaining para cresol by the action of a nitration mixture derived fromsulphuric acid and a nitrate salt, and used with considerable water.

Various other and ancillary objects and advantages will hereinafterbecome apparent.

We have discovered that our process is selective in that it effectsnitration of para cresol, but does not likewise nitrate isomericcresols. When our invention is practiced upon pure para cresol, it givesa clean product and a suitably high yield. However, when mixed isomersare used, such as one containing para cresol and 15% meta cresol, thereaction mass exhibits considerable oxidation and formation of tar orresin, without seriously altering the expected yield of meta nitro paracresol based on the actual content of para cresol initially employed.Further, we have found that the process does not nitrate pure orthocresol or pure meta cresol in any smooth manner comparable to itsnitration of pure para cresol. Therefore, we may use our process fornitrating either a pure para cresol or a mixture of cresol isomers, toobtain nitration of the para cresol isomer without similar orinterfering nitration of the other isomers. Although products ofoxidized or resinified character may be produced by the process frommeta or ortho isomers, or from minor reaction on the para isomer, theseonly create mechanical difficulties having to do largely with therecovery and purification of the desired meta nitrated para cresol. Theextent of these difficulties will therefore in part determine how muchimpurity may attend the para cresol in the original cresol, and alsodetermine to what extent the preferred process may be varied within thepermissible limits set forth. We have found it very practicable tonitrate either pure para cresol, or an impure para cresol containing asmuch as 15% of the meta isomer, without materially changing the yield orefficiency of the procedure based upon the chemical conversion of theactual content of pure para cresol. Purification of commercial 60-40mixed isomers to a point where composition is roughly 85% or more ofpara cresol and 15% or less of meta cresol is feasible and economicallypracticable for the present procedure. And likewise the presentprocedure is practicable for such an impure para cresol.

The process is distinctive in being carried out as an aqueous nitrationand by contact in a two-phase mixture with the cresol employed, paracresol being not completely if at all soluble in the aqueous nitratingsolution. As practically carried out, a dilute sulphuric acid solutioncontaining nitric acid is formed. This may be done in various ways as byadding nitric acid to dilute sulphuric acid, or adding a nitrate salt toa strong or dilute sulphuric acid, and diluting if required.Practically, an excess of a strong sulphuric acid and sodium nitrate aremixed. This forms nitric acid, sodium acid sulphate, and a weakersulphuric acid. This mixture is then poured into water, or into mixedice and water, to give quickly and directly a sufficiently coolnitrating liquid for the process. Then with heavy agitation, the pure orimpure cresol is slowly added in small stream, dropwise, or like mannerover an extended period to assure good mixing, such as an hours timemore or less, dependent upon the character of apparatus and theagitation. The time is not a critical factor, The two-phase mixtureresulting, is further agitated to assure completion of the reaction, anda period of two hours agitation after completion of the mixture issuitable. This time period is not critical with a suflicient agitationto assure good nitrating contact to complete the reaction. A heavy oillayer is then allowed to settle to the bottom, which layer is separatedfrom the upper layer, washed, and purified, preferably through a vaporphase as a distillate by steam distillation. This is the desired metanitro para cresol.

The temperature of the reaction may be from C. to 60 C. Preferably it islower at the beginning so that any increase by heat generated may keepit below the prescribed limit. It is further preferred to keep thetemperature between 30 C. and 40 C. Lower temperature seems to extendthe time of nitration reaction, permitting side reactions to proceed toofar, and this is more noticeable as the acid concentration is greater.

The following specific example gives a range of proportions of materialswhich may be employed.

Example 1 Parts by weight Sodium nitrate (or equivalent potassiumnitrate) 120 to 125 92% sulphuric acid 450 to 480 Water (600 parts ice)400 to 4000 Pure or crude para cresol 108 "lm-l'liw ll 01mwhere water is1400 to 1000 parts.

The foregoing formula is based upon 108 parts of the para cresol being amolecular quantity, or 1 mol of cresol. It may contain, for example 15%of admixed meta isomer, and the 108 parts or the formula may becalculated upon the mixed isomers or upon the content of the paraisomer. The amount of sodium nitrate or equivalent nitric acid set forthis about 1.4 to 1.5 mols for the 1 mol of cresol to be nitrated andtherefore there is an excess of nitric acid available for loss and forside reactions not desired. The amount of sulphuric acid is roughly 4.2to 4.5 mols, and only about 1.4 mols of this is lost as free acid ingenerating 1.4 to 1.5 mols of nitric acid from the nitrate salt. Excesssulphuric acid no doubt serves at this low dilution as the usualnitration catalyst. The large amount of water is necessary to minimizeresinification and oxidation arising from any undesired side reactionswhich may occur. The water item of the formula is from about 20 to about220 mols to which about 2 mols are added by the sulphuric acid item ofthe formula, and another mol of water is created in the nitration, suchadditions having practically no effect. Below 25 C. the nitrationproceeds very slowly. Above 60 C. certain ingredients of the mass burnup or are destroyed. The best results are obtained by following theprocedure as given above, within the preferred temperature limits of 30C. to 40 C. and with 1400 to 1600 parts of Water, which is from 78 to 89mols of water. Considering the added water above mentioned the preferrednitrating acid solution contains roughly from 80 to 90 mols of water forat least 1 mol of nitric acid, and a small amount of free sulphuricacid. A yield of 80% to 85% of meta nitro para cresol is thus obtainedbased upon the actual para cresol originally present in the rawmaterial.

However, it is to be understood that variations are permissible as willbe shown from the following tabulated examples, using a fixed quantityof 480 parts of 92% sulphuric acid, 125 parts of sodium nitrate, 108parts of cresol, and the variations as follows:

Based on content of para cresol.

The process is of great practical merit because it is applicable to bothpure para cresol, and to mixed isomers containing para cresol, withoutchange of procedure. Its selective action, in nitrating the para isomerand in not similarly nitrating the ortho and meta isomers, makes it avaluable procedure in that the product of using mixed cresols isrelatively free from mixed nitrated isomers resulting from simultaneousnitration of the mixed cresol isomers. For the economic use of theprocess, the practical limits of para cresol in mixed cresol isomers maybe fixed by many conditions entirely independent of the invention. Itwill thus appear to those skilled in the art, that the invention may beused in various ways with great chemical advantage as an isolationprocedure for para isomeric compounds within the scope of materialsinvolved, and with great economic advantage according to raw materialsavailable, and other economic factors.

We claim:

1. A process for the nitration of para cresol to form meta nitro paracresol, which comprises subjecting up to 1 mol of such cresol to theaction of an aqueous nitrating acid solution having at least 1 mol ofnitric acid, free sulphuric acid, and from 20 to 220 mols of water, saidaction being conducted at a temperature from 0 C. to 60 C.

2. A process for the nitration of the para cresol content of mixedcresol isomers to form meta nitro para cresol, which comprisessubjecting up to 1 mol of such mixed cresol isomers to the action of anaqueous nitrating acid solution having at least 1 mol of nitric acid,free sulphuric acid, and from 20 to 220 mols of water, said action beingconducted at a temperature from 0 C. to 60 C.

3. A process for the nitration of para cresol to form meta nitro paracresol, which comprises subjecting up to 1 mol of such cresol to theaction of an aqueous nitrating acid solution having at least 1 mol ofnitric acid, free sulphuric acid, and from 20 to 220 mols of water, saidaction being conducted at a temperature from 30 C. to 40 C.

4. A process for the nitration of the para cresol content of mixedcresol isomers to form meta nitro para cresol, which comprisessubjecting up to 1 mol of such mixed cresol isomers to the action of anaqueous nitrating acid solution having at least 1 mol of nitric acid,free sulphuric acid, and from 20 to 220 mols of water, said action beingconducted at a temperature from 30 C. to 40 C.

5. A process for the nitration of para cresol to form meta nitro paracresol, which comprises subjecting up to 1 mol of such cresol to theaction of an aqueous nitrating acid solution having at least 1 mol ofnitric acid, free sulphuric acid, and from 80 to 90 mols of water, saidaction being conducted at a temperature from 30 C. to 40 C.

6. A process for the nitration of the para cresol content of mixedcresol isomers to form meta nitro para cresol, which comprisessubjecting up to 1 mol of such mixed cresol isomers to the action of anaqueous nitrating acid solution having at least 1 mol of nitric acid,free sulphuric acid, and from 80 to 90 mols of water, said action beingconducted at a temperature from 30 C. to 40 C.

7. A process for the nitration of para cresol to form meta nitro paracresol, which comprises subjecting up to 1 mol of such cresol to theaction of an aqueous nitrating acid solution consisting of the reactionproducts of at least 1 mol of a nitrate salt, at least about 4 mols ofsulphuric acid calculated as 100%, and from 20 to 220 mols of water,said nitration being conducted at a temperature from 0 C. to 60 C.

8. A process for the nitration of the para cresol content of mixedcresol isomers to form meta nitro para cresol, which comprisessubjecting up to 1 mol of such mixed cresol isomers to the action of anaqueous nitrating acid solution consisting of the reaction products ofat least 1 mol of a nitrate salt, at least about 4 mols of sulphuricacid calculated as 100%, and from 80 to 90 mols of water, said nitrationbeing conducted at a temperature from 30 C. to 40 C.

9. A process for nitrating para cresol to form meta nitro para cresolwhich comprises mixing para cresol with an aqueous nitrating acidsolution containing sulphuric acid at from 0 C. to 60 C. whereby paracresol is converted to meta nitro para cresol as an oil in the spentnitrating acid solution, separating said oil from the said spent acidsolution, and purifying the separated oil through its vapor phase.

10. The method of making a separation of a para compound fromaccompanying isomeric compounds which consists in subjecting a mixtureof isomeric cresols containing a substantial amount of para cresol tothe action of an aqueous nitrating acid solution containing sulphuricacid at from 0 C. to 60 C. whereby para cresol is converted to metanitro cresol as an oil in. the spent nitrating acid solution and theisomeric cresol is largely converted to tar or resinous matter, andseparating the tar and resinous matter from the meta nitro para cresol.

11. The method of selectively treating para cresol in the presence of anisomeric cresol to form meta nitro para cresol substantially free fromisomers, which consists of subjecting the isomeric cresols to the actionat from 0 C. to 60 C. of an aqueous nitrating solution containingsulphuric acid, the action of the nitrating solution being selective tonitrate the para cresol isomer, and to convert the isomeric cresol intowaste matter separable from the resulting meta nitro para cresol.

ROBERT FRYE. GRADY M. ONEAL.

